Regeneration of a fixed-bed fischer-tropsch catalyst



Patented Sept. 2, 1952 etcjtsthirm LQ iA'fi XiiD'rtBI-i FI-SCHER' TRGPSCH GATALYST 'jiisepli- Ci Par, assignors'toGulf Res mas-g dam en" a Develoiilnerit" company; Pittsburgh, Par, 3;- corpdratioli of Delawar-.. v

iii-Whig: hiisucatiii" iiiiy'itz- 1949- Serial No. 104', s eiaims (Cl. 252-1 415) v i i This invention relates to a-methoq of regenerating solid synthesis catalysts; particularly asolid synthesis catalystdispbs'ed in ai fixed bed which has been employed-1 11 the SYfithi of-liidrocarbons by the reaction b'etweehcartcn-mohoxide and hydrogen; q

Several methodsdor carfying Ont the' -rac-tio'h between carbon monoxide and h drogen iii the presence of a solid synthesis catalyst have been proposed, including methods im olying' the use of a fixed bed of synthesis catalyst in which tern perature control is accomplished by means of indirect heat exchange elements}methods in which the} synthesis gasmixture is'conta'cted with the catalyst disposed ina fluidizdbediand methods operated on. the adiabatic principlewherein the ment costs are relatively:;l ow.-- lnorderzfor suchprocesses to be competitive-whowever; it is'important that the catalyst bej capable of-efiect'ive use over long periods of time-as fcat-alyst:changes represent a substantial-part of thecost-;of-opera'etion. The usual cycle-of operation of an'iiadiar' batiefixed bed process: com-prises -essentiallyeal ternate on- -strearn periodsduring; which hydro carbons are produced withsome lay-down: of-carbonaceons material on -thecatalyst and regeneration periods during; which-the; carbonaceous mafe' terial isburned oil The cycle may also include fiushingperiods and periods -forreduction of the catalyst. Itha-s been-*recogn-ized' thatvtotalftimer during which a catalyst-may be employedis dc pendehtu on the pressure-drop across the catalyst bed. When this pressure-drop becornes excessive; catalyst change is required. Anothenhnpertant factor afiecting the tirne .during ghich the -catalyst may be erriployedisthe' maximum terripera ture to which thecat'alyst" issfi-bjectdduring:

regeneration; If thisWrfiperatur -isvpe tted to go too high; both"the'physical and c emic'al make necessary change of catalyst" The present inlvention'isconce improved method of regefierating a fi'ied' bd bf diab'aticcatalyst which'has been einplbyed in 'a on-stream operation. a, Prior to making -the discovery upon which the'p'res'ent invention is based;

We had considered the-problem of'regenerating" the, catalyst as-one primarilyl'of effectingtem perature control: While-subj ectingithe catalystbed to a relatively low rate-of fiow'of -regeneration painted by: lossi-cfactiyity: Whether or not the gases sc to" reauc g st attritioir.-

w re

and an oxygen-ma ntaining:gas s r 7 low a temperature as could be einployedand yet accomplish burning ofi' or the catalyst eposit; thisway' controllifigthe xna fn'iirfi H rhpera tilreofthe catalyst bed' a in heating" compression costs. -We"-d1scb i ered when operating in'this ni'anrier 'thataivh il fegerieiaiti' efie'ctedy an increase t across'the' bed deylo'p d: Ih r 4 ressur' drop is indicativecit-physical deterio the catalyst; and may or .mayhot be'ae'co activity ofthe cataiysti is refill bed; in creasein pressuredrcpirequires catalyst change becauseoperation of: :the'f. process" becomes: ifn economical; due to excessive costs of forcing an adequate diiantity of ch'argethrofigh-the reactora-tit'he'high resistarlceto flovh 1 v We" were" then of theppinion that" an increase in this pressure drop-was fa necessafy concomi' tant to regenerating a fixed bedtofsynthesis catalysta-nd that the reductionjni the" tctal' tinie thata-catalystcould beemploxidicausedby-pres=' sure drop'l increases, duri'hgeregeneratioh iperio'ds wasr-a basic'ch aracteristic'offthis'type'iof process. Wee have i now" discovered, "however; that-"by heating.- a-mixture of? an"; inert gas and air oxy=" gem-containing gas" suchasiair toi a relatively high: temperature rior; to contacting-the gas" mixture with the bed of qise'd' synthsis 'catal'yst'f and: Controlling-the composition and rate or -now of: this gas -mixture sdtha'tthe; maximum mm: perature'} difference"v in fthe catalystbed at any time; during regene'rati'onisi'less thah'fi 00 Pl; 7 preferablyi less -tharf26o? FL," ffe'ctiv regriela tion of-- the catalyst" canbeaccbmplishedwitfi he or very little; increasejin the pressure dropz across the catalyst bed; rnakes, possible, the use" of the catalyst oyerlongex periods of '-'time':than' had formerly been;possible ='-'Qf ji "sa iiizz tur v leas '650? f betweenatduttto' ah aloe er'ably between alddu The mamm um-temperatfi thecatalysthed is?raise" at r generationeycle shourdnocbealcove Miam -1150" F. and preferably should be between about 900 and about 1000 F.

To maintain these temperature conditions, the composition of the regeneration gas mixture and the rate of flow of this mixture are mutually controlled so that the desired maximum temperature is not exceeded and the temperature diiference between the inlet temperature and the maximum temperature is less than 300 F. Since the time required for the regeneration is a factor catalyst had been formed in a compression pelleting machine into cylindrical pellets about A,

affecting the economics of the process, we prefer to operate so that the temperature diiierence referred to is not less than 100 F. Especially valuable results are obtained by'preheating the regeneration gas mixture to a temperature between about 700" and about 800 F. and controlling the composition and rate of flow of this mixture so that the maximum temperature reached at any point in the catalyst bed at any time during the regeneration does not exceed 1000 IE. and preferably lies within the range of about 900? to 1000 F., and the temperature difference between the preheat temperature and the maximum temperature'is between about 170 and about 260 F.

In practicing the present process in accordance with a preferred manner of proceeding, the regeneration is started by initially flowing in contact with the catalyst bed a gas consisting entirely or substantially entirely of inert constituents preheated tov a temperature of about 700 to about 800 F. When the catalyst bed has been heated-to; about the temperature of this initial gas mixture, air is added to the gas at a rate such that the maximum, temperature in the catalyst bed. does not exceed 1000 F. The amount of air in the regeneration gas mixture is increased as the regeneration proceeds so as to burn, off the less easily combustible portions of the carbonaceous deposit. Thus, while the regeneration gas in the early stages of regeneration Will consist very largely of inert. constituents, towards the end of the regeneration the regeneration gas may consist solely of air. The velocity of the regeneration gas through the bed, or, stated in another way, the total volume of regeneration gas passed through the bed per unit time, is controlledso as to maintain the temperature of the bed. This control may take the form of maintaining the velocity constant while adjusting the composition so as to obtain the desired temperature conditions, or the velocity may bevaried so as to assist positively in the temperature control. For example, the velocity of regeneration gasv through the bed is preferably greater during the middle portion of the regeneration period when maximum burning is being accomplished than at the beginning or end of this period. The regeneration is considered to have been completed when the temperature of the catalyst bed approaches the preheat temperature of the regeneration gas.

The present process is applicable to the regeneration of the solid synthesis catalysts as a class but we have found that especially effective results are obtained when the'catalyst is an iron catalyst. A suitable type of iron catalyst is one prepared by precipitation of iron oxide and is employed in the form of pellets. This catalyst is especially effective in certain types of synthesis processes when in the reduced or partially reduced state. When a reduced or partially reduced catalyst is employed, the regeneration. operation will be followed by a stage wherein the inch in diameter and 2; inch in height.

1400 cc. of this catalyst weighing about 2700 grams were charged toa reactor about 3 inches in diameterforming a fixed bed about 11 inches in height. The reactor was designed for adiabatic operation since it. consisted simply of a reactor shell, a bottom foraminous catalyst support, and

, means for preventing heat loss from the catalyst bed to the atmosphere.

The catalyst was then dried by passing inert gas, specifically hydrogen, over it at a drying temperature; for example, a temperature of the order of; 220 to 250 F. The dried catalyst was then partially reduced by passing heated, hydrogen into contact with it until the amount of water formed indicated that the desired extent of reduction had been attained; in this case 10.9 percent reduced from, the oxide. The catalyst was then employed in the synthesis of hydrocarbons in a process comprising charging to the reactor maintained at a pressure of about pounds per square inch'a reactor feed consisting of a fresh feed gas composed of hydrogen and carbon monoxide in a mol ratio of about. 32:1. and a recycled gas obtained by subjecting; the reaction products to condensation at a temperature of about 40? F. and the reactor pressure, the portion of the reaction products remaining in vapor format this temperature constituting the recycled gas. The volume ratio of recycled gas to fresh-feed was maintained at about 9:1. This catalyst was employed in three cycles consisting of a cycle I which comprised an on-stream period (time when the catalyst is contacted with synthesis gas) of 97 hours and a regeneration period in which the regeneration was carried out in accordance with the procedure described herein, 'a cycle II which comprised an on-stream' period "of 496.7 hours and a regeneration' period, a cycleIII which comprised an onstream period of 307"hours and a' regeneration period, and a final on-stream period of 330 hours after which'the testop'eration was discontinued because adequate data; had been obtained.

To illustrate 'thespeciflc manner; of carrying out the regeneration, the third regeneration period will be described more in detail. Throughout regeneration theregeneration 'gas introduced into the catalyst bed'waspreheated to a temperature of about 755 F; The regeneration was begun by introducing a gas consisting of nitrogen and a verysmall amount of air andthe relative amount of air to nitrogen was increased throughout the regeneration period until at the endof the period the. regeneration gas consisted of air. At the end of 25'hours the regeneration had been completed and the catalyst bed was ready for partial reduction. 'The changes made in the composition of the regeneration gas and the maximum temperature of the catalyst bed are given inthe. following table. It will be understood that the 'maximum temperature of the catalyst bed will'be' the temperature of the hottest zone in the'bed, which is conventionally referred to as a hot spot."

I Table. I:

. U H,ot Ai Nitro e n Time, Hours cu. ftJhr. emit/hr; Temper.-v

S. T. P. S."'P.'P. atIJre, v

Under he e. c ndit on the. r ssu rop through the catalyst bed was increased. so little durin the rese e a ienperiod ha it. s arel detectable. It will be. noted that the maximum temperature of the catalyst bed in this case was 990 F. and therefore the temperature difference between the inlet temperature and this. maximum temperature was 235 F. In the other regeneration periods on this catalyst the results obtained were similarto those described. Thus, in the first regeneration period the inlet temperature Was' 765 I 1, the maximum catalyst bed temperature during the regeneration was 960 F., giving a temperature difference of 195 F. In the second regeneration period the inlet temperature was 760 F., the maximum catalyst bed temperature was 975 F. and the temperature difference was 215 F. In each case the pressure drop in-. crease across the catalyst bed was barelydetectit The data given in the following Table II show the. advantages 'of'the present .process as compared with the practice involving introducing the regeneration gas at 'a relatively low temperature. In each case given inthe table, the catalyst was a partially reduced iron oxide catalyst and the regeneration gas comprised an inert gas and air as described. Catalyst D of Table II is the catalyst the regeneration in cycle III on catalyst C in-v volvedv too. high a temperature gradient and therefore caused an increase in pressure drop,

thev other regenerations were carried out under 5; satisfactory conditions so that the life of the catalyst was extended. In thecaseof catalyst D, as previously-indicated, the runwas discontinued because sufficient information had been obtained.

By proceeding-as described, effective regeneration' of othersynthesis catalystscan be accomplished. While, as previously stated, the process is especially satisfactory when employed for the regeneration of iron synthesis catalysts, which may be promoted or unpromoted, it also may be employed with advantage for "the regeneration of other.synthesiscatalysts such as nickel and cobalt or their oxides. I v

Itw-ill be understood by those skilled in the art that any gas which isinert to the catalyst can be employed for admixture with the oxygencontaining gas to form the regeneration gas. Flue gas, for example, issuitable and the flue gas used may be thatproduced in'the regeneration. In this case,--the-'oif-gases from the re-' generation are cooled-tothe desired inlet te.. perature, and then-recycled to 'the reactor.

The term-adiabatic as employed herein has its customary meaning whenapplied to. fixed bed catalytic processes. Thus, the heat used in the process is either supplied in v the-gases chargeddistinguishedf frorn afixed bed reactor provided withheat exchange, tubes orthe like in that in the latter type reactorheat is both supplied and removed by the heat exchange elements.

Obviously many modifications and variations of the invention as hereinabove set forth may be made without departing'from the spirit and of th example given bov scope thereof and therefore only such limitations Table II Quantity of Maximum Pressure Drop Through Catalyst Bed (p. s. 1.) Regeneration lgiegeigra- BCgtai lyst Tempera- Gas 512M83- on as e em ure mum ressure Catalyst Cycle T Inlet Igor Diizeg ence M xi 0 t I1%rop During emp. F. ing e- Prior to a mum n-s ream Net egenera ion generation During Reafter Re- (cu. ftJhr.

generation generation generation crease S. T. P.)

980 "ii s6 010+ "6.' "613 6T6 "ibifi 1, 000 170 0. 0+ 0.1 0.05 0. 0+ 99. 2 1, 140 385 0. 10 0.30 0.20 0. 1 146. 8 l, 000 250 0. 20 0. 45 71. 7 960 195 0.00 0. l5 0. 0+ 0. 0+ 86. 7 975 215 0.0+ 0. 05 0. 05 0. 0+ 80. 9 990 235 0. 1 0. 30 0. 10 0.0+ 87. 6

1 No on-stream period after regeneration.

2 No regeneration because of high pressure drop prior to regeneration.

8 No regeneration.

The results given in the foregoing table are indicative of those obtainable by practice of the present process. The total on-stream time for the catalysts was catalyst A, 765 hours; catalyst B, 889 hours; catalyst C, 1362 hours; and catalyst D, 1230 hours. The methods of regeneration employed in the cases of catalysts A and B are shown by the data to have limited the time during which these catalysts could be used. While moved from the catalyst bed substantially only with the exit gases, which comprises continuouslyintroducing into the bed of contaminated catalyst a, mixture of an inert gasand an oxygencontaining gas at an inlet temperature of about 650 to about 850 F., flowing said mixture through said catalyst/bed whereby the, carbonaceous deposit on said catalyst is burned off, and limiting the maximum temperature attained in the catalyst bed by controlling the ratioof'inert gas to oxygen and the rate of flow of saidigaseous' mixture to maintain -a temperature difference between said inlet temperature and the'maximum temperature of the catalyst bed of less than about 300F. i 1

2. A process in accordance with claim 1 in which the maximum :temperature during regeneration is between about 900 and about :1000 F. s 3. A process in accordance with claim '1 in which the synthesis, catalystis an iron synthesis catalyst. i.

v 4. A process of regenerating a fixed bed of iron synthesis catalyst; which is contaminated with carbonaceous deposits fromuse in the synthesis of hydrocarbons bythe reaction between carbon monoxide and hydrogen, under conditionssuch that heat evolved in the regeneration is removed from the catalyst bed substantially only with the exit gases, which comprisescontinuously introducing into the bed or contaminated catalyst a mixture of an inert gas and air at atemperature of about 650 to about850 F, flowing said mixture through said catalyst bed whereby the carbonaceous deposit on said catalyst is burned off, and limiting the maximum temperature attained in the catalyst bed by controlling the ratio of inert gas to air andthe rate of iiowof said gaseous mixture to, maintain a temperature difference between said inlet temperature'and the maximum temperature of the catalyst bed of less than about 260 1 r 5. A process in accordance with claim 4 in which the composition: and rate of flow of the mixture of inert gas and air are controlled to produce a maximum temperature in the catalyst bed during regeneration of between about 900 and about 1000 F.

6. A process of regenerating a fixed bed of iron synthesis catalyst which is contaminated with carbonaceous deposits from use in the synthesis of hydrocarbon by the reaction between carbon monoxide and hydrogen, under conditions such that heat evolved in the regeneration is removed from the catalyst bed substantially only with the exit gases, which comprises continuously introducing into the bed of contaminated catalyst a mixture of an inert gas and air at an inlet temperature within the range of about 700 to about 800 F., flowing said mixture through said catalyst bed whereby the carbonaceous deposit on said catalyst is burned off, and limiting the maximum temperature attained in the catalyst bed to between about 900 and 1000" F. by controlling the ratio of inert gas to air and the rate of flow of said gaseous mixture to maintain a temperature' difference between said inlet temperature andthe maximum temperature of the catalyst bed of between about and about 260 F.

JOSEPH C. EASLY.

HUGH L. KEILNER.

REFERENCES CITED The following references are of record in the file of this patent: I

UNITED STATES PATENTS Number Gunness Mar. 1, 1949. 

1. THE PROCESS OF REGENERATING A FIXED BED OF SOLID SYNTHESIS CATALYST WHICH IS CONTAMINATED WITH CARBONACEOUS DEPOSITS FROM USE IN THE SYNTHESIS OF HYDROCARBONS BY THE REACTION BETWEEN CARBON MONOXIDE AND HYDROGEN, UNDER CONDITIONS SUCH THAT HEAT EVOLVED IN THE REGENERATION IS REMOVED FROM THE CATALYST BED SUBSTANTIALLY ONLY WITH THE EXIT GASES, WHICH COMPRISES CONTINUOUSLY INTRODUCING INTO THE BED OF CONTAMINATED CATALYST A MIXTURE OF AN INERT GAS AND AN OXYGENCONTAINING GAS AT AN INLET TEMPERATURE OF ABOUT 650* TO ABOUT 850* F., FLOWING SAID MIXTURE THROUGH SAID CATALYST BED WHEREBY THE CARBONACEOUS DEPOSIT ON SAID CATALYST IS BURNED OFF, AND LIMITING THE MAXIMUM TEMPERATURE ATTAINED IN THE CATALYST BED BY CONTROLLING THE RATIO OF INERT GAS TO OXYGEN AND THE RATE OF FLOW OF SAID GASEOUS MIXTURE TO MAINTAIN A TEMPERATURE DIFFERENCE BETWEEN SAID INLET TEMPERATURE AND THE MAXIMUM TEMPERATURE OF THE CATALYST BED OF LESS THAN ABOUT 300* F. 